commit 75e84ab906ef8935cff3df3d8929f1bafea81599
Author: Lukas Wunner <lukas@wunner.de>
Date:   Thu Jun 18 13:00:32 2015 +0200

    perf tools: Fix build breakage if prefix= is specified
    
    Invoking Makefile.perf with prefix= breaks the build since Makefile.perf
    hands that variable down to Makefile.build where it overrides
    
        prefix       := $(subst ./,,$(OUTPUT)$(dir)/)
    
    leading to errors like this:
    
        No rule to make target '/usrabspath.o', needed by '/usrlibperf-in.o'
    
    Signed-off-by: Lukas Wunner <lukas@wunner.de>
    Acked-by: Jiri Olsa <jolsa@kernel.org>
    Cc: David Ahern <dsahern@gmail.com>
    Fixes: c819e2cf2eb6f65d3208d195d7a0edef6108d5
    Link: http://lkml.kernel.org/r/5582c48a.84a22b0a.a918.5285SMTPIN_ADDED_MISSING@mx.google.com
    Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/build/Makefile.build b/tools/build/Makefile.build
index 10df572..98cfc38 100644
--- a/tools/build/Makefile.build
+++ b/tools/build/Makefile.build
@@ -94,12 +94,12 @@ obj-y        := $(patsubst %/, %/$(obj)-in.o, $(obj-y))
 subdir-obj-y := $(filter %/$(obj)-in.o, $(obj-y))
 
 # '$(OUTPUT)/dir' prefix to all objects
-prefix       := $(subst ./,,$(OUTPUT)$(dir)/)
-obj-y        := $(addprefix $(prefix),$(obj-y))
-subdir-obj-y := $(addprefix $(prefix),$(subdir-obj-y))
+objprefix    := $(subst ./,,$(OUTPUT)$(dir)/)
+obj-y        := $(addprefix $(objprefix),$(obj-y))
+subdir-obj-y := $(addprefix $(objprefix),$(subdir-obj-y))
 
 # Final '$(obj)-in.o' object
-in-target := $(prefix)$(obj)-in.o
+in-target := $(objprefix)$(obj)-in.o
 
 PHONY += $(subdir-y)